Stroke is a major cause of death and disability, of either embolic or hemodynamic origin. Many strokes are preceded by transient ischemic attacks (TIAs) generally thought to be caused by emboli consisting of one or more thrombi occluding an intracranial blood vessel, followed by lysis and fragmentation of the clot in the process of recanalization. The origin of these emboli may be from ulcerations of stenotic segments of the internal carotid artery, or from other sites such as the heart and great vessels. The primary goal is to develop a non-invasive means for detecting and counting the number of emboli passing through the middle cerebral artery of patients presenting symptoms of TIA or stroke. This will be accomplished by developing a method to allow monitoring of a patient over an extended period through the use of a transcranial Doppler. Specifically, we will modify existing commercial transcranial Doppler equipment by taking audio-signal output and running it through specially designed FFT spectral analysis at a high processing rate. We have shown that emboli in the middle cerebral artery can be easily detected by the gross modifications they produce in the Doppler flow spectrum. Ultimately, we wish to determine the relationship between thrombus size and Doppler signature. This will allow us to determine the effects of surgery and medical treatment on thrombogenesis as well as provide the ability to study the natural frequency of thrombogenesis in patients with carotid lesions. This may allow discrimination of which lesions are producing emboli and are potentially dangerous.